The Yangtze River basin in China is home to about 322 species of fish and 169 species of amphibians, creating a series of diverse ecosystems that rely primarily on the flow of Asia's longest river. It is also home to 400 million Chinese, who depend on its fertile deltas for food and on the Yangtze's 700 tributaries for navigation and energy.

Currently, over 46 large dams (over 60 meters high) are planned or are under construction on the Yangtze. "The dams will cause considerable environmental damage and trigger a decline in the rich biodiversity of the basin," says Rivers at Risk: Dams and The Future of Freshwater Ecosystems, a new report prepared by World Wildlife Fund (WWF) and the World Resources Institute (WRI).

The report grapples with a fundamental contradiction concerning the issue of dams and water use and ecosystem stewardship, especially in the developing world. According to the U.N., more than 2 billion people globally lack access to electricity, 1.1 billion do not have safe drinking water, and 2.4 billion still require adequate sanitation services. Dams provide much needed fresh water for domestic use, crop irrigation, as well as for the mitigation of floods, and hydropower for millions.

While dams are seen by developing world governments as an easy solution to the shortages of electricity and fresh water, Rivers at Risk claims that dams devastate fisheries, destroy wetlands, and ultimately compromise fragile habitats that are not only home to innumerable species of freshwater fish, mammals, and water birds, but also provide essential goods and services to humans, particularly the poor.

A fragmentation analysis done by WRI in 2000 revealed that 60% of the world's 227 largest rivers are moderately to severely altered by dams, water diversions, and canals. According to Rivers at Risk, more than 45,000 large dams are operational in over 150 countries and approximately another 1,500 are under construction.

This new report represents the most comprehensive analysis of planned dams mapped by basin on a global scale. "We combined WRI's analytical capacity to develop global and regional-level indicators with WWF's on-the-ground knowledge in key areas to provide information and feedback for the report," said Carmen Revenga, leader of WRI's work on water and marine fisheries.

Delicate habitats like those in the Yangtze basin, Rivers at Risk contends, are irreparably damaged by large dam construction. Species such as the Chinese alligator (the most threatened crocodile species in the world), the Yangtze River dolphin or baiji (the most threatened cetacean in the world), and the finless porpoise (the only freshwater-adapted porpoise in the world), will continue to see serious population declines and possibly become extinct as the Yangtze River continues to be dammed and modified.

While dams are touted as cure-all solutions to the energy and water issues affecting populations in the developing world, the report asserts that dams often fail to live up to expectations. A report from the World Commission on Dams states that 40 to 80 million people - including 10 million in the Yangtze River basin - have been displaced due to global dam construction. The rapid decline of certain fisheries, because of altered flows from dam construction, also adversely affect the livelihood of millions of people that depend on fisheries as their only source of protein.

Rivers at Risk claims that a re-examination of the alternatives to dams and the consideration of ecological effects during the planning process for large dams can ensure that people receive the water and energy they need, while protecting the environment.

"Building a dam away from the main stem of a river system, creating appropriate fish passes for native species, and replicating the natural streamflow of a river can reduce the ecological harm caused by large dams," said Carmen Revenga. "Rainwater harvesting, alternative crops, mini- and micro-hydro schemes, and wind power are environmentally friendly alternatives to the creation of dams."

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by Peter Denton (features@wri.org), the managing editor of WRI Features, an international news features service on environment and development issues.